Method

Preheat oven to 220˚C/Gas Mark 7. Once the oven is up to temperature, take the pastry sheet out of the fridge. Unroll it and cut into 4 equal sized rectangles.

You only need 2 of them, wrap the other 2 back up and keep in the fridge for a few days for another meal (see cook’s note).

Put 2 of the rectangles on a nonstick baking sheet. Use a sharp knife to score a border around the pastry, about 1.5cm in from the edge. Use a fork to prick the middle part several times (this helps prevent it puffing up too much).

Bake for 12-15 minutes, until it’s a pale golden colour, but not quite cooked through. Meanwhile, wash the watercress and asparagus. Bend the asparagus stalks one at a time until part of the base snaps off (this indicates where they start to be tough). Discard the bases or save them (see cook’s note).

Cut the stalk tops off the fennel bulb, saving any bright green feathery fronds to use as garnish. Cut the bulb in half lengthways. Chop out the tough core at the base, in a triangular shape. Very finely slice the rest. Transfer it to a medium to large bowl.

Cut a small slice off the top and bottom of the orange. Ideally using a small serrated knife, cut down and round to remove the skin and pith, then between each membrane to release the segments.

If you find this tough, peel, finely slice then cut the slices in half or quarter’s. Add the orange segments to the fennel. Squeeze any juice from the leftover membranes into the bowl. Add 2 tablespoons of good olive oil. Season with salt and pepper.

After 12-15 minutes, remove the pastry from the oven. Carefully push down any pastry that’s risen in the middle part, leaving the puffed up edge. Leave it to cool for 5 minutes. Meanwhile, separate the egg yolks and whites. Discard the whites or save (see cook’s note).

Put the yolks in a bowl. Crumble in the blue cheese. Add the crème fraîche. Trim the asparagus spears if needed, so they’ll fit lengthways in the middle of the pastry bases later on. Finely slice any leftover trimmed asparagus. Add them to the egg and blue cheese.

Season (use little or no salt as the cheese will be salty) and stir together. Carefully spoon the egg mixture into the middle of each piece of pastry. Spread the mixture out to cover the pastry. Lay the asparagus spears on top (if the spears are thick, slice them lengthways in half first).

Use your fingers to dab them with a little olive oil. Season with pepper. Bake for about 15 minutes, until the pastry is crisp and golden. Meanwhile, chop the hazelnuts into smaller pieces. Once the tarts are cooked, toss the watercress with the hazelnuts, fennel (plus any fronds) and orange. Serve alongside the tarts.

Cooks notes

Keep the leftover pastry to make another tart, or cut into strips, twist and sprinkle over some finely grated cheese and bake to make some puffed cheesy straws. Use the leftover egg whites to make meringues. Egg whites will freeze well if you don’t want to use them immediately. The bottom of your asparagus stalks can also be saved and used to make a stock, good for risotto or pasta dishes.